Polyspectral fluorescent lamp

ABSTRACT

The inner surface of a tubular fluorescent lamp has at least two separate and distinct phosphor coatings on different longitudinal segments thereof, the color of light emitted by each phosphor coating differing from that of the other. The lamp is rotatably mounted in a fixture having an aperture parallel to the lamp. By suitable rotation of the lamp within the fixture, light from either of the phosphors may be preferentially directed through the aperture for illumination purposes.

United States Patent Schreurs 1 1 July 1 1, 1972 541 POLYSPECTRALFLUORESCENT LAMP 3,354,343 11/1967 Myers ..313/113 [72] lnventor: WillyP. Schreurs, Danvers, Mass. FOREIGN PATENTS OR APPLICATIONS 1 1Assigneer 11 Electric Mum 1,4s9,1o1 6/1967 France ..313/115 22 Filed:March 12 1970 I l Primary ExaminerHerman Karl Saalbach PP -No: 18,815Assistant Examiner-Saxfield Chatmon, Jr.

Attorney-Norman J. OMalley and James Theodosopoulos [52] U.S. Cl..313/109, 313/111, 240/1 [51] Int. Cl. .1101] 61/20, l-lOlj 61/44ABSTRACT [58] Field of Search ..313/109, I10, 111, 1 5351114, The innerSurface of a tubular fluorescent lamp has at least 3 I I 5 two separateand distinct phosphor coatings on different 1oned gitudinal segmentsthereof, the color of light emitted by each [56] Referemes phosphorcoating differing from that of the other. The lamp is UNITED STATESPATENTS rotatably mounted in a fixture having an aperture parallel tothe lamp. By suitable rotation of the lamp within the fixture, 2,135,7321 1/1938 Randall et al ..313/ 109 li h f m either of the phosphors maybe preferentially ,3 1 946 Morehouse 1 3/109 directed through theaperture for illumination purposes. 2,317,265 4/1943 Foerste et al......3l3/l09 3,379,917 4/1968 Menelly ..313/109 3Clainm,2DrawingliguresPATENTEDJUL 1 1 1972 WILLY P. SCHREURS INVENTOR BYgw vT ATTORNEY 1POLYSPECTRAL FLUORESCENT LAMP BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to fluorescent lamps andparticularly to such lamps having different phosphors on longitudinalsegments thereof capable of emitting light of different colors.

2. Description of the Prior Art For some lighting purposes it isdesirable to employ a lamp that is capable of supplying illumination thecolor of which can be varied. For example, such a lamp may be used toobserve the appearance of textiles which have been dyed, say, for use inmanufacturing a suit or dress, under illumination that corresponds tonatural daylight or incandescent light or a particular type offluorescent light. Such a material may be pleasing to the eye whenviewed in daylight, but may be dull and unattractive when viewed underincandescent light. The reason for this is that incandescent light isdeficient in colors found at the short wavelength end of the colorspectrum, that is, the blues, violets and greens, and materialpredominating in such colors is dulled when viewed under incandescentlight. Thus, it would be desirable to observe dyed cloth under alllighting conditions in which it could be used in order to determine thatits visual appearance would be satisfactory.

Another use of variable color illumination is in cosmetics application,where the color of such cosmetics should be pleasing whether veiwedunder natural daylight conditions or under incandescent or fluorescentlight.

In the past, commercially available lamps for such applications wereoften used in fixtures in which different colored filters could beinterposed between the lamp and the subject to be illuminated. Such anarrangement was not always entirely satisfactory, since such filterssubstantially reduced the total illumination falling on the subject. Inaddition, a single light source could not usually supply sufficientspectral energy of the necessary wavelengths to satisfactorily match thecolor of different types of illumination.

The use of separate light sources to provide each type of desiredillumination resulted in apparatus that was generally awkward and spaceconsuming.

It is the purpose of this invention to provide a single, fluorescentlamp that is capable of supplying light of eitherof at least twodifferent colors.

SUMMARY OF THE INVENTION A fluorescent lamp in accordance with thisinvention has at least two separate phosphor coatings on the innersurface of a tubular lamp envelope and on different longitudinalsegments thereof. The color of light emitted by each phosphor differsfrom that of the other and can be designed to closely match the color ofa predetermined type of illumination. For example, one of the phosphorscan be compounded to emit light of a color that closely matches that ofincandescent light; the other phosphor can be of a type that emits lightof a color that matches natural daylight.

In operation such a lamp is disposed inside an enclosing fixture whichhas a narrow aperture along one surface thereof. The aperture isproximate the lamp and is substantially parallel thereto so that most ofthe light passing through the aperture emanates from the phosphorcoating that faces the aperture. The lamp is rotatably mounted withinthe fixture so that either phosphor coating may be presented to theaperture depending on the type of illumination desired. Suitableelectrical connecting means are disposed in the fixture for the purposeof connecting the lamp to an external source of electrical power.

In order that the desired illumination emanate substantially only fromthe proximate phosphor coating, the width of the aperture is kept smalland preferably does not substantially exceed the width of the chordsubtended by the arc of the proximate phosphor coating. For example, ifa lamp has two phosphor coatings, each covering 180 of the lampcircumference the width of the aperture should not substantially exceedthe lamp diameter. And if a lamp has three phosphor coatings of l20coverage each, the aperture should not exceed about 86 percent of thelamp diameter; for four 90 coatings, the maximum aperture width would beabout 70 percent of the lamp diameter. Of course the width of theaperture should not be so narrow that only an undesirably small fractionof the total light output of the lamp can pass therethrough and fall onthe subject desired to be illuminated.

Preferably, the inside surface of the fixture is substantiallynon-reflective in order to prevent any significant amount of lightemitted by the distant phosphor coating from being reflected by thefixture and passing out through the aperture. However if the lampdiameter exceeds about 50 percent of the inside diameter of the fixture,where the fixture is substantially circular, then the lamp itself willblock most of the reflected light from passing out through the aperture.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of afluorescent lamp having two different phosphor coatings on the innersurface of the lamp envelope.

FIG. 2 is an illustrative drawing of such a lamp within an aperturedfixture.

DESCRIPTION OF THE PREFERRED EMBODIMENT In a specific embodiment of afluorescent lamp in accordance with this invention, as shown in FIG. 1,a tubular glass envelope 1 has phosphor coatings 2 and 3 longitudinallydisposed on the inner surface thereof. Each coating covers about of thelamp circumference. One phosphor coating,

say, phosphor 2, is of a type that emits light the color of whichclosely resembles the color of light from an incandescent lamp. Theother phosphor coating, phosphor 3, emits light of a color that closelyresembles the color of average natural daylight.

Phosphor coating 2 is deposited on glass envelope 1 from a The blend hasa mean particle diameter of 10 microns and is dispersed in a vehicleconsisting of nitrocellulose binder in butyl acetate solvent.

Glass envelope 1 is washed, prior to coating, and then allowed to dry. Asufficient amount of the suspension is then poured into envelope 1,envelop 1 being tilted slightly above a horizontal position, to form apool of suspension in the bottom of the envelope when envelope 1 isplaced in a horizontal position. Envelope 1 is then slowly rotated untilabout l80 of its surface is coated by the suspension. The excesssuspension is then poured off and the coating allowed to dry with theenvelope in a vertical position.

Phosphor coating 3 is deposited on the remaining 180 surface of envelope1 in a similar manner as coating 2 from a suspension containing a blendof the following materials:

Wt. 7t Calcium-strontium-magnesium orthophosphate, tin activated 35 7:Barium-titanium pyrophosphate 47 7c Calcium-magnesium tungstate, leadactivated l5 7: Zinc orthosilicate, manganese activated 3 This blend isdispersed in a vehicle consisting of ethyl cellulose binder in xylolsolvent, xylol being used as the solvent "since it will not dissolve thenitrocellulose binder of coating 2 at the point where coating 3contacts, but does not overlap, coating 2. After the second phosphor hasbeen allowed to dry, the coated envelope is heated for three minutes at600C. to burn off the binder, and to cause the phosphor particles toadhere to the surface of the envelope.

The lamp is then completed by conventional methods in cluding the stepsof disposing electrodes and bases at each end of the envelope,exhausting the envelope, filling with an arcsustaining filling includingmercury and then sealing.

In operation the phosphors transform the radiation from the mercury arcinto visible radiation. Phosphor coating 2 emits light of a color thatclosely resembles the color of light from an incandescent lamp. Thepurpose of the yellow titanium oxide, a non-phosphor material, incoating 2 is to filter the high peaks of violet and blue light emittedby the mercury arc and thereby improve the resemblance to incandescentlight. Phosphor coating 2 has a Color Rendering Index of 94.0 percent ata color temperature standard of 2,700K.

Phosphor coating 3 emits light of a color that closely matches the colorof average natural daylight. It has a Color Rendering Index of 89percent at a color temperature standard of 6,750K;

In operation the lamp is axially mounted inside an elongated tubularfixture 4, as illustrated in FIG. 2, having about double the diameter ofthe lamp. An aperture 5 having a width about half the lamp diameterextends along the length of the fixture parallel to the lamp. The lampis rotatably mounted within the fixture so that either phosphor coating2 or 3 may be presented to the aperture depending on whetherincandescent type illumination or average natural daylight illuminationis desired. Thus by means of this single lamp, an object may be viewedunder either daylight or incandescent light.

If it is desired to introduce a third color into the light emission ofthe lamp, then phosphor coatings 2 and 3 can each be reduced to 120coverage, and a third phosphor coating can be deposited on the remaining120 lamp surface. Such a third phosphor can comprise a phosphor used inparticular types of commercially available fluorescent lamps, such asWhite, Cool White, Natural White and the like.

Before deposition of the third phosphor coating, the first two coatingswould preferably be baked at the previously mentioned heatingconditions, to render them resistant to the solvent in the thirdphosphor coating.

it is not necessary, for pruposes of this invention, that the phosphorcoatings be designed to emit light of a color which closely matches thatof other natural or artificial lumination. A lamp capable of emittinglight of either to two or three or more colors may be desired for thepurpose of illuminating a painting or other art object and for varyingfrom time to time the color of the illuminating light and thus theartistic effect of the object.

For example, the phosphor of coating 2 an emitter of incandescent typelight, may be one of the coatings deposited on the lamp surface. Asecond phosphor coating prepared to emit red colored light, can consistof the red-emitting components of phosphor coating 2, namely, thetin-activated barium-strontium-magnesium orthophosphate and themanganese-activated magnesium fluorogermanate. And a third phosphorcoating designed to emit blue colored light, can consist of theblueemitting components of phosphor coating 2, namely, the titaniumpyrophosphate and the tin-activated strontium pyrophosphate. I

In a lamp having these three phosphor coatings, the color of lightavailable for illumination through the fixture aperture can be variedconsiderably by presenting different ratios of adjoining phosphorcoatings to the aperture. in addition, brightness control could beobtained by depositing a reflectortype coating, such as is shown in US.Pat. No. 3,225,241 entitled Aperture Fluorescent Lamp issued to Spenceret al. on

Dec. 21, 1965, between parts of the phosphor coatings and the lampenvelope. Lamp brightness could be decreased by increasing the amount ofthe reflector coating that is presented to the aperture.

Although the preferred embodiments of the polyspectral lamp of theinstant invention are described for use within an apertured fixture,such lamps may also be used in an ordinary fluorescent fixture which ismade non-reflecting or may even be used without a fixture. In the lattercase suitable means would be used to energize the lamp and support it atits ends. The desired type of illumination would be obtained bypositioning the lamp so that light from the corresponding phosphorcoating would shine directly on the object to be illuminated. The otherphosphor coating would radiate its light in the opposite direction.

Iclaim:

1. A fluorescent lamp comprising: an elongated glass envelope;electrodes disposed at either end of said envelope; an arc-sustainingfilling disposed within said envelope; and at least two separatephosphor coatings disposed on the inner surface of said envelope, saidphosphor coatings being disposed on separate longitudinal segmentsthereof and each phosphor coating designed to emit light of a differentcolor than the other and wherein substantially the entire inner surfaceof said envelope is covered by said phosphor coatings, wherebyillumination of at least two difierent colors may be obtained from saidlamp by axial rotation thereof in relation to a region to beilluminated.

2. The lamp of claim 1 wherein one of said phosphor coatings is anemitter of incandescent type light and the other phosphor coating is anemitter of daylight type light.

3. The lamp of claim 1 comprising, in addition, an elongated fixturehaving an aperture, said lamp being rotatably mounted within saidfixture and said aperture being substantially parallel to said lamp, thelength of said aperture being about equal to the length of said lamp,the width of said aperture being less than the length of a chordsubtending the arc of the phosphor coating having the greatercircumferential coverage on said envelope.

2. The lamp of claim 1 wherein one of said phosphor coatings is anemitter of incandescent type light and the other phosphor coating is anemitter of daylight type light.
 3. The lamp of claim 1 comprising, inaddition, an elongated fixture having an aperture, said lamp beingrotatably mounted within said fixture and said aperture beingsubstantially parallel to said lamp, the length of said aperture beingabout equal to the length of said lamp, the width of said aperture beingless than the length of a chord subtending the arc of the phosphorcoating having the greater circumferential coverage on said envelope.